1. Field of the Invention
The present invention relates to an operational amplifier that can be used as a charge amplifier, and more particularly to a differential operational amplifier capable of differentially outputting a differential input signal by differentially amplifying the differential input signal to a broader bandwidth.
2. Discussion of the Related Art
When constructing probe-based data storage utilizing a piezoelectric sensor manufactured through MEMS (Micro Electro Mechanical System) design techniques, a miniscule intensity of charge outputted from the piezoelectric sensor may be amplified to a sufficient amount of voltage using a charge amplifier.
Typically, an operational amplifier is largely used for the charge amplifier. In order to align a plurality of piezoelectric cantilevers manufactured by the MEMS design techniques with multiple charge amplifiers, and integrate the same, a low power and high density circuit design technique is required.
An operational amplifier used as a charge amplifier must amplify a small sized input signal to a high gain and show an excellent characteristic relative to various noises. Therefore, the operational amplifier used as the charge amplifier must be preferably constructed in a differential structure to minimize the influence of noise.
A common mode feedback circuit must be essentially disposed in the operational amplifier in order to stabilize an output signal of the operational amplifier. Moreover, in order to design an operational amplifier capable of detecting a continuously-timed signal, not a discretely-timed signal, a continuously-timed common mode feedback circuit must be disposed. At the same time, a signal frequency amplified by the operational amplifier must be compensated to obtain a sufficiently enough phase margin and to secure circuit stability.
A typical Miller compensation is widely used as one of the methods for compensating the frequency of the operational amplifier. However, when a differential-type operational amplifier employed for the Miller compensation is utilized for use that requires a relatively high closed circuit amplification rate as in the charge amplifier, a frequency response bandwidth relative to allowable consumption power comes to be degraded to make it difficult to operate at a high speed. It is therefore essential to require a frequency compensation method capable of expanding a bandwidth that does not consume an additional power.